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checkout: -m (--merge) uses autostash when switching branches

Browse Source 
When switching branches with "git checkout -m", local modifications
can block the switch.  Teach the -m flow to create a temporary stash
before switching and reapply it after.  On success, only "Applied
autostash." is shown.  If reapplying causes conflicts, the stash is
kept and the user is told they can resolve and run "git stash drop",
or run "git reset --hard" and later "git stash pop" to recover their
changes.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Harald Nordgren
2026-04-09 19:17:15 +00:00
committed by Junio C Hamano
parent 79324a330e
commit c3a8de96dd
10 changed files with 371 additions and 142 deletions
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60
Documentation/git-checkout.adoc
View File

@@ -251,20 +251,19 @@ working tree, by copying them from elsewhere, extracting a tarball, etc.
are different between the current branch and the branch to
which you are switching, the command refuses to switch
branches in order to preserve your modifications in context.
However, with this option, a three-way merge between the current
branch, your working tree contents, and the new branch
is done, and you will be on the new branch.
+
When a merge conflict happens, the index entries for conflicting
paths are left unmerged, and you need to resolve the conflicts
and mark the resolved paths with `git add` (or `git rm` if the merge
should result in deletion of the path).
With this option, the conflicting local changes are
automatically stashed before the switch and reapplied
afterwards. If the local changes do not overlap with the
differences between branches, the switch proceeds without
stashing. If reapplying the stash results in conflicts, the
entry is saved to the stash list. Resolve the conflicts
and run `git stash drop` when done, or clear the working
tree (e.g. with `git reset --hard`) before running `git stash
pop` later to re-apply your changes.
+
When checking out paths from the index, this option lets you recreate
the conflicted merge in the specified paths. This option cannot be
used when checking out paths from a tree-ish.
+
When switching branches with `--merge`, staged changes may be lost.
`--conflict=<style>`::
The same as `--merge` option above, but changes the way the
@@ -578,39 +577,44 @@ $ git checkout mytopic
error: You have local changes to 'frotz'; not switching branches.
------------
You can give the `-m` flag to the command, which would try a
three-way merge:
You can give the `-m` flag to the command, which would carry your local
changes to the new branch:
------------
$ git checkout -m mytopic
Auto-merging frotz
Switched to branch 'mytopic'
------------
After this three-way merge, the local modifications are _not_
After the switch, the local modifications are reapplied and are _not_
registered in your index file, so `git diff` would show you what
changes you made since the tip of the new branch.
=== 3. Merge conflict
When a merge conflict happens during switching branches with
the `-m` option, you would see something like this:
When the `--merge` (`-m`) option is in effect and the locally
modified files overlap with files that need to be updated by the
branch switch, the changes are stashed and reapplied after the
switch. If this process results in conflicts, a stash entry is saved
and made available in `git stash list`:
------------
$ git checkout -m mytopic
Auto-merging frotz
ERROR: Merge conflict in frotz
fatal: merge program failed
Your local changes are stashed, however, applying it to carry
forward your local changes resulted in conflicts:
- You can try resolving them now. If you resolved them
successfully, discard the stash entry with "git stash drop".
- Alternatively you can "git reset --hard" if you do not want
to deal with them right now, and later "git stash pop" to
recover your local changes.
------------
At this point, `git diff` shows the changes cleanly merged as in
the previous example, as well as the changes in the conflicted
files. Edit and resolve the conflict and mark it resolved with
`git add` as usual:
------------
$ edit frotz
$ git add frotz
------------
You can try resolving the conflicts now. Edit the conflicting files
and mark them resolved with `git add` as usual, then run `git stash
drop` to discard the stash entry. Alternatively, you can clear the
working tree with `git reset --hard` and recover your local changes
later with `git stash pop`.
CONFIGURATION
-------------

33
Documentation/git-switch.adoc
View File

@@ -123,18 +123,19 @@ variable.
`-m`::
`--merge`::
If you have local modifications to one or more files that are
different between the current branch and the branch to which
you are switching, the command refuses to switch branches in
order to preserve your modifications in context. However,
with this option, a three-way merge between the current
branch, your working tree contents, and the new branch is
done, and you will be on the new branch.
+
When a merge conflict happens, the index entries for conflicting
paths are left unmerged, and you need to resolve the conflicts
and mark the resolved paths with `git add` (or `git rm` if the merge
should result in deletion of the path).
If you have local modifications to one or more files that
are different between the current branch and the branch to
which you are switching, the command normally refuses to
switch branches in order to preserve your modifications in
context. However, with this option, the conflicting local
changes are automatically stashed before the switch and
reapplied afterwards. If the local changes do not overlap
with the differences between branches, the switch proceeds
without stashing. If reapplying the stash results in
conflicts, the entry is saved to the stash list. Resolve
the conflicts and run `git stash drop` when done, or clear
the working tree (e.g. with `git reset --hard`) before
running `git stash pop` later to re-apply your changes.
`--conflict=<style>`::
The same as `--merge` option above, but changes the way the
@@ -217,15 +218,15 @@ $ git switch mytopic
error: You have local changes to 'frotz'; not switching branches.
------------
You can give the `-m` flag to the command, which would try a three-way
merge:
You can give the `-m` flag to the command, which would carry your local
changes to the new branch:
------------
$ git switch -m mytopic
Auto-merging frotz
Switched to branch 'mytopic'
------------
After this three-way merge, the local modifications are _not_
After the switch, the local modifications are reapplied and are _not_
registered in your index file, so `git diff` would show you what
changes you made since the tip of the new branch.

138
builtin/checkout.c
View File

@@ -17,7 +17,6 @@
#include "merge-ll.h"
#include "lockfile.h"
#include "mem-pool.h"
#include "merge-ort-wrappers.h"
#include "object-file.h"
#include "object-name.h"
#include "odb.h"
@@ -30,6 +29,7 @@
#include "repo-settings.h"
#include "resolve-undo.h"
#include "revision.h"
#include "sequencer.h"
#include "setup.h"
#include "submodule.h"
#include "symlinks.h"
@@ -783,8 +783,10 @@ static int merge_working_tree(const struct checkout_opts *opts,
struct tree *new_tree;
repo_hold_locked_index(the_repository, &lock_file, LOCK_DIE_ON_ERROR);
if (repo_read_index_preload(the_repository, NULL, 0) < 0)
if (repo_read_index_preload(the_repository, NULL, 0) < 0) {
rollback_lock_file(&lock_file);
return error(_("index file corrupt"));
}
resolve_undo_clear_index(the_repository->index);
if (opts->new_orphan_branch && opts->orphan_from_empty_tree) {
@@ -797,14 +799,18 @@ static int merge_working_tree(const struct checkout_opts *opts,
} else {
new_tree = repo_get_commit_tree(the_repository,
new_branch_info->commit);
if (!new_tree)
if (!new_tree) {
rollback_lock_file(&lock_file);
return error(_("unable to read tree (%s)"),
oid_to_hex(&new_branch_info->commit->object.oid));
}
}
if (opts->discard_changes) {
ret = reset_tree(new_tree, opts, 1, writeout_error, new_branch_info);
if (ret)
if (ret) {
rollback_lock_file(&lock_file);
return ret;
}
} else {
struct tree_desc trees[2];
struct tree *tree;
@@ -814,6 +820,7 @@ static int merge_working_tree(const struct checkout_opts *opts,
refresh_index(the_repository->index, REFRESH_QUIET, NULL, NULL, NULL);
if (unmerged_index(the_repository->index)) {
rollback_lock_file(&lock_file);
error(_("you need to resolve your current index first"));
return 1;
}
@@ -846,82 +853,8 @@ static int merge_working_tree(const struct checkout_opts *opts,
ret = unpack_trees(2, trees, &topts);
clear_unpack_trees_porcelain(&topts);
if (ret == -1) {
/*
* Unpack couldn't do a trivial merge; either
* give up or do a real merge, depending on
* whether the merge flag was used.
*/
struct tree *work;
struct tree *old_tree;
struct merge_options o;
struct strbuf sb = STRBUF_INIT;
struct strbuf old_commit_shortname = STRBUF_INIT;
if (!opts->merge)
return 1;
/*
* Without old_branch_info->commit, the below is the same as
* the two-tree unpack we already tried and failed.
*/
if (!old_branch_info->commit)
return 1;
old_tree = repo_get_commit_tree(the_repository,
old_branch_info->commit);
if (repo_index_has_changes(the_repository, old_tree, &sb))
die(_("cannot continue with staged changes in "
"the following files:\n%s"), sb.buf);
strbuf_release(&sb);
/* Do more real merge */
/*
* We update the index fully, then write the
* tree from the index, then merge the new
* branch with the current tree, with the old
* branch as the base. Then we reset the index
* (but not the working tree) to the new
* branch, leaving the working tree as the
* merged version, but skipping unmerged
* entries in the index.
*/
add_files_to_cache(the_repository, NULL, NULL, NULL, 0,
0, 0);
init_ui_merge_options(&o, the_repository);
o.verbosity = 0;
work = write_in_core_index_as_tree(the_repository,
the_repository->index);
ret = reset_tree(new_tree,
opts, 1,
writeout_error, new_branch_info);
if (ret)
return ret;
o.ancestor = old_branch_info->name;
if (!old_branch_info->name) {
strbuf_add_unique_abbrev(&old_commit_shortname,
&old_branch_info->commit->object.oid,
DEFAULT_ABBREV);
o.ancestor = old_commit_shortname.buf;
}
o.branch1 = new_branch_info->name;
o.branch2 = "local";
o.conflict_style = opts->conflict_style;
ret = merge_ort_nonrecursive(&o,
new_tree,
work,
old_tree);
if (ret < 0)
die(NULL);
ret = reset_tree(new_tree,
opts, 0,
writeout_error, new_branch_info);
strbuf_release(&o.obuf);
strbuf_release(&old_commit_shortname);
if (ret)
return ret;
rollback_lock_file(&lock_file);
return 1;
}
}
@@ -1166,6 +1099,9 @@ static int switch_branches(const struct checkout_opts *opts,
struct object_id rev;
int flag, writeout_error = 0;
int do_merge = 1;
int created_autostash = 0;
struct strbuf old_commit_shortname = STRBUF_INIT;
const char *stash_label_ancestor = NULL;
trace2_cmd_mode("branch");
@@ -1203,10 +1139,31 @@ static int switch_branches(const struct checkout_opts *opts,
do_merge = 0;
}
if (old_branch_info.name)
stash_label_ancestor = old_branch_info.name;
else if (old_branch_info.commit) {
strbuf_add_unique_abbrev(&old_commit_shortname,
&old_branch_info.commit->object.oid,
DEFAULT_ABBREV);
stash_label_ancestor = old_commit_shortname.buf;
}
if (do_merge) {
ret = merge_working_tree(opts, &old_branch_info, new_branch_info, &writeout_error);
if (ret && opts->merge) {
create_autostash_ref_silent(the_repository,
"CHECKOUT_AUTOSTASH");
created_autostash = 1;
ret = merge_working_tree(opts, &old_branch_info, new_branch_info, &writeout_error);
}
if (ret) {
apply_autostash_ref_with_labels(the_repository,
"CHECKOUT_AUTOSTASH",
new_branch_info->name,
"local",
stash_label_ancestor);
branch_info_release(&old_branch_info);
strbuf_release(&old_commit_shortname);
return ret;
}
}
@@ -1216,8 +1173,29 @@ static int switch_branches(const struct checkout_opts *opts,
update_refs_for_switch(opts, &old_branch_info, new_branch_info);
if (opts->conflict_style >= 0) {
struct strbuf cfg = STRBUF_INIT;
strbuf_addf(&cfg, "merge.conflictStyle=%s",
conflict_style_name(opts->conflict_style));
git_config_push_parameter(cfg.buf);
strbuf_release(&cfg);
}
apply_autostash_ref_with_labels(the_repository, "CHECKOUT_AUTOSTASH",
new_branch_info->name, "local",
stash_label_ancestor);
discard_index(the_repository->index);
if (repo_read_index(the_repository) < 0)
die(_("index file corrupt"));
if (created_autostash && !opts->discard_changes && !opts->quiet &&
new_branch_info->commit)
show_local_changes(&new_branch_info->commit->object,
&opts->diff_options);
ret = post_checkout_hook(old_branch_info.commit, new_branch_info->commit, 1);
branch_info_release(&old_branch_info);
strbuf_release(&old_commit_shortname);
return ret || writeout_error;
}

30
builtin/stash.c
View File

@@ -590,8 +590,11 @@ static void unstage_changes_unless_new(struct object_id *orig_tree)
die(_("could not write index"));
}
static int do_apply_stash(const char *prefix, struct stash_info *info,
int index, int quiet)
static int do_apply_stash_with_labels(const char *prefix,
struct stash_info *info,
int index, int quiet,
const char *label1, const char *label2,
const char *label_ancestor)
{
int clean, ret;
int has_index = index;
@@ -643,9 +646,9 @@ static int do_apply_stash(const char *prefix, struct stash_info *info,
init_ui_merge_options(&o, the_repository);
o.branch1 = "Updated upstream";
o.branch2 = "Stashed changes";
o.ancestor = "Stash base";
o.branch1 = label1 ? label1 : "Updated upstream";
o.branch2 = label2 ? label2 : "Stashed changes";
o.ancestor = label_ancestor ? label_ancestor : "Stash base";
if (oideq(&info->b_tree, &c_tree))
o.branch1 = "Version stash was based on";
@@ -717,17 +720,31 @@ restore_untracked:
return ret;
}
static int do_apply_stash(const char *prefix, struct stash_info *info,
int index, int quiet)
{
return do_apply_stash_with_labels(prefix, info, index, quiet,
NULL, NULL, NULL);
}
static int apply_stash(int argc, const char **argv, const char *prefix,
struct repository *repo UNUSED)
{
int ret = -1;
int quiet = 0;
int index = use_index;
const char *label1 = NULL, *label2 = NULL, *label_ancestor = NULL;
struct stash_info info = STASH_INFO_INIT;
struct option options[] = {
OPT__QUIET(&quiet, N_("be quiet, only report errors")),
OPT_BOOL(0, "index", &index,
N_("attempt to recreate the index")),
OPT_STRING(0, "ours-label", &label1, N_("label"),
N_("label for the upstream side in conflict markers")),
OPT_STRING(0, "theirs-label", &label2, N_("label"),
N_("label for the stashed side in conflict markers")),
OPT_STRING(0, "base-label", &label_ancestor, N_("label"),
N_("label for the base in diff3 conflict markers")),
OPT_END()
};
@@ -737,7 +754,8 @@ static int apply_stash(int argc, const char **argv, const char *prefix,
if (get_stash_info(&info, argc, argv))
goto cleanup;
ret = do_apply_stash(prefix, &info, index, quiet);
ret = do_apply_stash_with_labels(prefix, &info, index, quiet,
label1, label2, label_ancestor);
cleanup:
free_stash_info(&info);
return ret;

18
sequencer.c
View File

@@ -4766,15 +4766,23 @@ static int apply_save_autostash_oid(const char *stash_oid, int attempt_apply,
strvec_push(&store.args, stash_oid);
if (run_command(&store))
ret = error(_("cannot store %s"), stash_oid);
else if (attempt_apply)
fprintf(stderr,
_("Your local changes are stashed, however, applying it to carry\n"
"forward your local changes resulted in conflicts:\n"
"\n"
" - You can try resolving them now. If you resolved them\n"
" successfully, discard the stash entry with \"git stash drop\".\n"
"\n"
" - Alternatively you can \"git reset --hard\" if you do not want\n"
" to deal with them right now, and later \"git stash pop\" to\n"
" recover your local changes.\n"));
else
fprintf(stderr,
_("%s\n"
_("Autostash exists; creating a new stash entry.\n"
"Your changes are safe in the stash.\n"
"You can run \"git stash pop\" or"
" \"git stash drop\" at any time.\n"),
attempt_apply ?
_("Applying autostash resulted in conflicts.") :
_("Autostash exists; creating a new stash entry."));
" \"git stash drop\" at any time.\n"));
}
return ret;

24
t/t3420-rebase-autostash.sh
View File

@@ -61,18 +61,30 @@ create_expected_failure_apply () {
First, rewinding head to replay your work on top of it...
Applying: second commit
Applying: third commit
Applying autostash resulted in conflicts.
Your changes are safe in the stash.
You can run "git stash pop" or "git stash drop" at any time.
Your local changes are stashed, however, applying it to carry
forward your local changes resulted in conflicts:
- You can try resolving them now. If you resolved them
successfully, discard the stash entry with "git stash drop".
- Alternatively you can "git reset --hard" if you do not want
to deal with them right now, and later "git stash pop" to
recover your local changes.
EOF
}
create_expected_failure_merge () {
cat >expected <<-EOF
$(grep "^Created autostash: [0-9a-f][0-9a-f]*\$" actual)
Applying autostash resulted in conflicts.
Your changes are safe in the stash.
You can run "git stash pop" or "git stash drop" at any time.
Your local changes are stashed, however, applying it to carry
forward your local changes resulted in conflicts:
- You can try resolving them now. If you resolved them
successfully, discard the stash entry with "git stash drop".
- Alternatively you can "git reset --hard" if you do not want
to deal with them right now, and later "git stash pop" to
recover your local changes.
Successfully rebased and updated refs/heads/rebased-feature-branch.
EOF
}

195
t/t7201-co.sh
View File

@@ -210,6 +210,201 @@ test_expect_success 'checkout --merge --conflict=diff3 <branch>' '
test_cmp expect two
'
test_expect_success 'checkout --merge --conflict=zdiff3 <branch>' '
git checkout -f main &&
git reset --hard &&
git clean -f &&
fill a b X d e >two &&
git checkout --merge --conflict=zdiff3 simple &&
cat <<-EOF >expect &&
a
<<<<<<< simple
c
||||||| main
b
c
d
=======
b
X
d
>>>>>>> local
e
EOF
test_cmp expect two
'
test_expect_success 'checkout -m respects merge.conflictStyle config' '
git checkout -f main &&
git reset --hard &&
git clean -f &&
test_config merge.conflictStyle diff3 &&
fill b d >two &&
git checkout -m simple &&
cat <<-EOF >expect &&
<<<<<<< simple
a
c
e
||||||| main
a
b
c
d
e
=======
b
d
>>>>>>> local
EOF
test_cmp expect two
'
test_expect_success 'checkout -m skips stash when no conflict' '
git checkout -f main &&
git clean -f &&
fill 0 x y z >same &&
git stash list >stash-before &&
git checkout -m side >actual 2>&1 &&
test_grep ! "Created autostash" actual &&
git stash list >stash-after &&
test_cmp stash-before stash-after &&
fill 0 x y z >expect &&
test_cmp expect same
'
test_expect_success 'checkout -m skips stash with non-conflicting dirty index' '
git checkout -f main &&
git clean -f &&
fill 0 x y z >same &&
git add same &&
git checkout -m side >actual 2>&1 &&
test_grep ! "Created autostash" actual &&
fill 0 x y z >expect &&
test_cmp expect same
'
test_expect_success 'checkout -m stashes and applies on conflicting changes' '
git checkout -f main &&
git clean -f &&
fill 1 2 3 4 5 6 7 >one &&
git checkout -m side >actual 2>&1 &&
test_grep ! "Created autostash" actual &&
test_grep "Applied autostash" actual &&
fill 1 2 3 4 5 6 7 >expect &&
test_cmp expect one
'
test_expect_success 'checkout -m with mixed staged and unstaged changes' '
git checkout -f main &&
git clean -f &&
fill 0 x y z >same &&
git add same &&
fill 1 2 3 4 5 6 7 >one &&
git checkout -m side >actual 2>&1 &&
test_grep ! "Created autostash" actual &&
test_grep "Applied autostash" actual &&
fill 0 x y z >expect &&
test_cmp expect same &&
fill 1 2 3 4 5 6 7 >expect &&
test_cmp expect one
'
test_expect_success 'checkout -m stashes on truly conflicting changes' '
git checkout -f main &&
git clean -f &&
fill 1 2 3 4 5 >one &&
test_must_fail git checkout side 2>stderr &&
test_grep "Your local changes" stderr &&
git checkout -m side >actual 2>&1 &&
test_grep ! "Created autostash" actual &&
test_grep "resulted in conflicts" actual &&
test_grep "git stash drop" actual &&
git stash drop &&
git reset --hard
'
test_expect_success 'checkout -m produces usable stash on conflict' '
git checkout -f main &&
git clean -f &&
fill 1 2 3 4 5 >one &&
git checkout -m side >actual 2>&1 &&
test_grep "recover your local changes" actual &&
git checkout -f main &&
git stash pop &&
fill 1 2 3 4 5 >expect &&
test_cmp expect one
'
test_expect_success 'checkout -m stashes on staged conflicting changes' '
git checkout -f main &&
git clean -f &&
fill 1 2 3 4 5 >one &&
git add one &&
git checkout -m side >actual 2>&1 &&
test_grep ! "Created autostash" actual &&
test_grep "resulted in conflicts" actual &&
test_grep "git stash drop" actual &&
git stash drop &&
git reset --hard
'
test_expect_success 'checkout -m applies stash cleanly with non-overlapping changes in same file' '
git checkout -f main &&
git reset --hard &&
git clean -f &&
git checkout -b nonoverlap_base &&
fill a b c d >file &&
git add file &&
git commit -m "add file" &&
git checkout -b nonoverlap_child &&
fill a b c INSERTED d >file &&
git commit -a -m "insert line near end of file" &&
fill DIRTY a b c INSERTED d >file &&
git stash list >stash-before &&
git checkout -m nonoverlap_base 2>stderr &&
test_grep "Applied autostash" stderr &&
test_grep ! "resulted in conflicts" stderr &&
git stash list >stash-after &&
test_cmp stash-before stash-after &&
fill DIRTY a b c d >expect &&
test_cmp expect file &&
git checkout -f main &&
git branch -D nonoverlap_base &&
git branch -D nonoverlap_child
'
test_expect_success 'checkout -m -b skips stash with dirty tree' '
git checkout -f main &&
git clean -f &&
fill 0 x y z >same &&
git checkout -m -b newbranch >actual 2>&1 &&
test_grep ! "Created autostash" actual &&
fill 0 x y z >expect &&
test_cmp expect same &&
git checkout main &&
git branch -D newbranch
'
test_expect_success 'switch to another branch while carrying a deletion' '
git checkout -f main &&
git reset --hard &&

2
t/t7600-merge.sh
View File

@@ -914,7 +914,7 @@ test_expect_success 'merge with conflicted --autostash changes' '
git diff >expect &&
test_when_finished "test_might_fail git stash drop" &&
git merge --autostash c3 2>err &&
test_grep "Applying autostash resulted in conflicts." err &&
test_grep "your local changes resulted in conflicts" err &&
git show HEAD:file >merge-result &&
test_cmp result.1-9 merge-result &&
git stash show -p >actual &&

12
xdiff-interface.c
View File

@@ -325,6 +325,18 @@ int parse_conflict_style_name(const char *value)
return -1;
}
const char *conflict_style_name(int style)
{
switch (style) {
case XDL_MERGE_DIFF3:
return "diff3";
case XDL_MERGE_ZEALOUS_DIFF3:
return "zdiff3";
default:
return "merge";
}
}
int git_xmerge_style = -1;
int git_xmerge_config(const char *var, const char *value,

1
xdiff-interface.h
View File

@@ -55,6 +55,7 @@ void xdiff_set_find_func(xdemitconf_t *xecfg, const char *line, int cflags);
void xdiff_clear_find_func(xdemitconf_t *xecfg);
struct config_context;
int parse_conflict_style_name(const char *value);
const char *conflict_style_name(int style);
int git_xmerge_config(const char *var, const char *value,
const struct config_context *ctx, void *cb);
extern int git_xmerge_style;